how can design the ptat ?

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hello:

how can decide the parameters of the mos-transistor? the circuit schematic is in the razavi's book "the design of analog integrate circuit" page 325, 11.31(b) .


i want to get a 50uA , i got the value , but the value change a lot when i choose the different power such as when i change the power from 3v to 2.7v ,the value change from 50u to 35u ,why ?



thank you !!!
 

Whitout seeing the schematic I guess either some of your transistors are operating in the linear region or their channel length is much too short.
 

now ,i got a value 50 which do not change too much with the power, but it change a lot with the temperture, such as it change from 40 to 70u when the temperture change from -25 to 125,


why ?
 

maybe yous circuit model changed with temperature,
if you want get good current ,maybe VBG add BIAS is best
 

maybe i need to choose one vbg add bias circuit to get a good current source ,

the ptat changed too much with the temperture !!!1
 

use current bias the circuit
 

maybe amp is operating in the linear region.
 

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